Prosopis spp. (tree, shrub)

Ecology Distribution Management Info Impact Info References and Links Contacts

General Impact The four main species that have presented problems as weeds world-wide are P. glandulosa and P. velutina in more subtropical regions and P. juliflora and P. pallida in the truly tropical zone. Prosopis is now a declared weed over millions of square kilometres of arid and semiarid lands, where it drastically reduces the production of forage plants, threatening the livelihoods of ranchers (Pasiecznik 2001). In its native range, Prosopis increases the density of vegetation. Environmental disturbances typically caused by humans, such as over-grazing and increased bush fire rates (due to poor land management), stimulate Prosopis growth and aggravating its effects. In its introduced range the species is much more aggressive. There are dense infestations in areas including but not limited to: Africa (the Sahel region, Sudan, Ethiopia, Kenya, Namibia, South Africa, Eritrea), India, Australia, St Helena (Ascension), and Brazil (Zimmerman Pers. Comm. 2003). Prosopis species have received international attention because of their impact on open grassland and woodland ecosystems. They form impenetrable thickets, smother native vegetation and hinder some primary production sectors. Around 1985 the USA experienced production losses of some $200-500 million per year from mesquite infestations (Agriculture & Resource Management Council of Australia & New Zealand, 2000).          Location Specific Impacts: Sahel (Africa)   Reduction in native biodiversity: In spite of the species providing a range of services to local communities there have been cases where negative impacts on the environment have been recorded. Prosopis appears to naturally colonise dry-zone areas, the niche previously occupied by native woody species, populations of which had been greatly reduced due to exploitation. Please follow this link to read more on the FAO-Netherlands Partnership Programme on Agro-Biodiversity's Survey of the effects of Prosopis introduction in Sahelian Africa (FAO, undated). Australia   Competition: Mesquites form thickets that out-compete ground vegetation monopolising light, water and nutrients and other resources. This has an impact on the diversity and abundance of native fauna (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Economic/Livelihoods: Primary production is affected due to (i) the increased difficulty and expense of mustering stock, (ii) the impeded access of stock to water, (iii) the increased water loss from watering points and (iv) the reduced pasture production (Infestations can reduce grass production by up to 90%) and subsequent reduction of the land’s carrying capacity. The lower cattle numbers and produce as a result of mesquite infestations has caused economic losses of an estimated $25,000/year in NW Queensland. Like prickly acacia, mesquites reduce the aesthetic value and biodiversity of open grassland and open woodlands in Northern Australia. This may translate to losses to sectors depending on tourists (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Habitat alteration: Mesquites (Prosopis species) are one of northern Australia’s worst weeds. They are a group of thorny shrubs and trees that aggressively replace grasslands and thorn-less shrubland (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Human nuisance: Prosopis thorns (which may be up to 7.5cm long) damage vehicle tyres and may wound animals or people (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Interaction with other invasive species: Feral pigs gather and feed on seedpods further damaging natural vegetation in the vicinity (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Modification of hydrology: Evidence from South Africa suggests that mesquite have a dramatic effect on the water table and surface runoff (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Modification of natural benthic communities: Potentially, all river systems and tidal estuaries in the northern rangeland areas of Australia are vulnerable to infestation by mesquites (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Other: Mesquite has been found in Bladensberg and Welford National Parks in SW Queensland and Moorinya National Park in central Queensland, but is subject to ongoing control programs. Its presence in conservation areas in other parts of Australia has not been recorded (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Physical disturbance: Exacerbates and accelerates soil erosion (Agriculture & Resource Management Council of Australia & New Zealand, 2000). Reduction in native biodiversity: Open grasslands and native thorn-less woody shrublands are vulnerable to being changed to thorny shrublands, with potentially large effects on native fauna and flora (Agriculture & Resource Management Council of Australia & New Zealand, 2000). South Africa   Modification of hydrology: Exacerbates and accelerates soil erosion. Evidence from South Africa suggests that mesquites may have a dramatic effect on the water table and surface runoff (Agriculture & Resource Management Council of Australia & New Zealand, 2000). United States (USA)   Economic/Livelihoods: Fifteen years ago, the USA experienced production losses of some $200-500 million per year from mesquite infestations (Agriculture & Resource Management Council of Australia & New Zealand, 2000).